WO2007054585A2

WO2007054585A2 - Method for indirectly monitoring a tire pressure

Info

Publication number: WO2007054585A2
Application number: PCT/EP2006/068440
Authority: WO
Inventors: Andreas Köbe; Vladimir Koukes; Markus Irth; Franko Blank; Christian Sussmann
Original assignee: Continental Teves Ag & Co. Ohg; Continental Aktiengesellschaft
Priority date: 2005-11-14
Filing date: 2006-11-14
Publication date: 2007-05-18
Also published as: WO2007054585A3; EP1948453A2; US20080243423A1; EP1948453B1; DE102006053826A1

Abstract

Disclosed is a method for indirectly monitoring a tire pressure, in which the rolling circumference of the tires is analyzed by determining rolling circumference analysis variables (ΔIAG, ΔSIDE, ΔAXLE) from currently determined and theoretical test variables describing the rotary movement of the wheels and analyzing a frequency of the natural oscillation behavior of at least one tire, at least one frequency analysis variable (fk) being determined. The analysis (A) of the rolling circumference and the analysis (C) of the natural frequency are evaluated while both analytical processes are evaluated (B) in a combined manner in order to issue a warning regarding a loss of tire pressure.

Description

Method for indirect tire pressure monitoring

The invention relates to a method according to the preamble of claim 1 and a computer program product.

In modern motor vehicles systems are increasingly used, which contribute to an active or passive protection of the occupants. Tire pressure monitoring systems protect vehicle occupants from vehicle damage caused, for example, by incorrect tire air pressure. Unmatched tire inflation pressure can, for example, increase tire wear and fuel consumption, or lead to a tire failure ("tire burst") Various tire pressure monitoring systems are already known which operate either on the basis of directly measuring sensors or by evaluating speed or vibration characteristics the vehicle wheels detect an abnormal tire pressure.

From DE 100 58 140 Al a so-called indirectly measuring tire pressure monitoring system (DDS: Deflation Detection System) is known, which detects a tire pressure loss by evaluating the wheel rotational movement. 826 Bl, a tire pressure determining apparatus is known which determines a pressure loss in a tire based on tire vibrations.

WO 01/87647 A1 describes a method and a device for tire pressure monitoring which combines a tire pressure monitoring system based on the detection of wheel radii and a tire pressure monitoring system based on the evaluation of vibration characteristics.

From WO 05/072995 A1 a method for monitoring tire pressure is known, which improves an indirectly measuring tire pressure monitoring system by taking into account at least one torsional natural frequency in such a way that the reliable detection of an abnormal tire air pressure is increased.

The object of the invention is to provide a tire pressure monitoring system for a motor vehicle based on the evaluation of the wheel rotational movement and the tire vibrations, in which the reliability of the detection and warning of tire inflation pressure losses is increased.

This object is achieved by the method according to claim 1.

The invention is based on the idea of constructing the warning strategy both on the separate evaluation of a rolling circumference analysis of the tires and on a natural frequency analysis of the tires as well as on a combination of the two analyzes. When combining the rolling circumference analysis and the frequency analysis, alarm thresholds for each of the two analysis methods are preferably adjusted to the other method depending on the results, eg of analysis variables. This will improve the reliability of the alert. To adapt the warning threshold (s), the pressure loss analysis variables of the respective other method are particularly preferably used.

Likewise, it is preferred that, when combining both analysis methods, warning thresholds of each of the two analysis methods are selected as a function of the results of the respective other method and a correlation measure between the two analysis methods. The correlation measure describes to what extent rolling circumference analysis and frequency analysis describe the same image of one or more pressure losses at the wheels. Here too, the pressure loss analysis variables of the respective other method are particularly preferably used to adapt the warning threshold (s).

According to a preferred embodiment, in the combination of both analysis methods, wheel-individualized pressure loss analysis variables are determined in each case for rolling circumference analysis and frequency analysis. This makes possible a wheel-specific warning and a wheel-individual combination of the two analysis methods. Warning thresholds of each of the two analysis methods are particularly preferably selected as a function of the wheel-specific pressure loss analysis variables of the respective other method. According to a development of the invention, the warning thresholds are also changed as a function of the availability of the analysis variables. This reduces the risk of false alarms if an analytical method temporarily provides no or no reliable information.

Preferably, for at least one wheel, more preferably for each wheel, a combined wheel-individual pressure loss analysis quantity is determined from the pressure loss analysis variables of the rolling circumference analysis and frequency analysis of the same wheel. In this case, the warning thresholds or the common warning threshold of both analysis methods are particularly preferred. In addition, it is particularly preferred to determine the combined wheel-specific pressure loss analysis size based on a warning field. If the combined wheel-specific pressure loss analysis variable exceeds a threshold, then a pressure loss at the corresponding wheel can be decided.

In a further development of the invention, a warning regarding a tire pressure loss as a function of at least two, particularly preferably as a function of all, of the combined wheel-specific pressure loss analysis variables is output.

The warning preferably takes place on the basis of the maximum of the combined wheel-specific pressure loss analysis variables.

According to a further preferred embodiment, for at least one of the analysis variables, the rolling circumference analysis, the natural frequency analysis or the combination of the two nalyses, carried out a plausibility test of the specific value. For this purpose, the time course of the analysis size is considered. In this case, a rolling circumference analysis size, a frequency analysis size, a pressure loss analysis size or a combined pressure loss analysis size can be checked.

On the basis of the result of the plausibility check, a decision is preferably made as to whether there is a pressure loss or a stammering influence. As a result, false warnings, which are caused by Storeinflusse avoided.

In addition, the loading and / or a load change of the vehicle is determined according to a further preferred embodiment. This should be detected changes in the load, which may have an influence on the analysis sizes of the individual analysis methods, so as to avoid false alarms by changing the load.

Preferably, the loading and / or load change detection is achieved by linking at least one information of a rolling circumference analysis of the wheels with at least one information of a frequency analysis of the natural vibration behavior of at least one tire. According to the invention, this information already exists and thus no further sensors or the like are necessary for detecting a load change.

Advantageously, in the frequency analysis for at least one wheel a Maßgröße, which is a measure of the expression of the natural frequency, determined. Especially It is advantageous if such a size is determined for each wheel. The energy content of the spectrum in the region of the natural frequency is particularly preferably used as a measure. The measure size (s) or a ratio of measures are then used to detect the loading and / or change of cargo. Particularly preferred is the ratio of Maßgrößen between front and rear wheels used.

In a development of the invention, the detection of a loading and / or load change leads to a change in the warning threshold (s) of the analysis variables and / or to a compensation of the analysis variables. Advantageously, the load-dependent pressure loss analysis variables are compensated or the warning thresholds of the load-dependent pressure loss analysis are adjusted in size.

According to a further preferred embodiment, in particular in the frequency analysis, a temperature compensation of an analysis variable, in particular a frequency analysis large, at least one tire is performed. This has the advantage that the influence of the tire temperature on the tire can be taken into account. As a result, the risk of false alarm or Nichtwarngefahr is reduced at pressure loss when driving with high temperature fluctuations. A temperature compensation of a natural frequency of the tire determined by the frequency analysis is particularly preferably carried out.

In order to determine a temperature compensation variable, it is preferable to use a temperature coefficient calculated by means of a temperature model. fentemperatur used. The temperature compensation quantity for the frequency analysis is advantageously a quotient of the change of the frequency analysis variable to the temperature change.

Preferably, to learn the compensation quantity, the analysis quantity together with the calculated tire temperature is considered over one or more journeys. This ensures sufficient statistical relevance.

The temperature model preferably takes into account at least one of the following heat changes: heat flow through walkar-

of the tire (Q _Waik ), heat flow through convection

(Qc _onvect _on ) ι heat flow through radiation of the tire

(Q _Rad i _at i _on ) or heat flow through heat input of the vehicle

•

(Qv _eh i _c i _e c _ond i _t i _on ) • Preferably, the tire temperature is calculated from at least one of the heat ^¬ me changes, most preferably from the sum of all heat changes, by temporal integration.

In the temperature model, at least two of the following variables are advantageously taken into account: outside temperature, temperature in a control unit, engine intake air temperature, coolant temperature, engine temperature, brake temperature, service life of the vehicle, driving profile since the ignition is switched on, particularly preferably vehicle speed, yaw rate, lateral acceleration, drive torque and / or kilometers driven, environmental sensor information such as rain sensor and / or dew point sensor information. An advantage of the method according to the invention lies in the improved suppression or avoidance of false warnings or non-warnings in the event of pressure loss.

The invention also relates to a computer program product which defines an algorithm according to the method described above.

Further preferred embodiments will become apparent from the subclaims and the following description with reference to figures.

Show it

1 is a schematic block diagram of an exemplary method,

2 is a schematic block diagram of an embodiment for combining the two analysis methods,

3 shows a warning field for warning a wheel-individual pressure loss,

4 shows an influence of the correlation between rolling circumference analysis and natural frequency analysis on the warning thresholds in a warning field,

5 shows a warning strategy for warning a tire air pressure loss on the basis of four warning fields, 6 is a schematic block diagram of a temperature compensation in the frequency analysis, and

7 is a schematic block diagram of a tire temperature calculation.

The document WO 2005/072995 A1 "Method for indirect tire pressure monitoring" describes a system which concludes from the change of rolling circumference analysis variables in combination with changes of torsional natural frequencies of the tire to a pressure loss. By the method according to the invention the following problems of the known method are to be solved:

1. Availability of the system:

The two analysis methods (rolling circumference analysis and natural frequency analysis) have different requirements or conditions to be active and to provide reliable values. Warning thresholds which do not adjust to these different states of activity / availability result in an increased risk of false alarms or non-alarms in case of pressure loss.

2. Threshold influence:

The document WO 2005/072995 A1 deals with the case where the warning thresholds for the rolling circumference analysis variables are adjusted as a function of the correlation of the two pressure loss analysis variables (eg frequency shift and rolling circumference differential) and the absolute value of the frequency shift. An adaptation of the warning thresholds for the frequency shift (frequency analysis ße) is not disclosed.

3. Signal plausibility:

The analysis variables, in particular from the natural frequency analysis, are subject to statistical fluctuations and road influences. This can lead to e.g. a rapid natural frequency drop is detected by the algorithm without a pressure loss having occurred. This can lead to false warnings.

4. Loading:

The rolling circumference analysis size responds to increased loading in the same way as to a pressure loss. Accordingly, a distinction between an increased load and a pressure loss alone with values from the rolling circumference analysis is not possible. This leads in particular when learning with unloaded vehicle and later driving with loaded vehicle to an increased risk of mis-warning.

5. Temperature influence:

The tire temperature has an influence on the pressure in the tire (increased temperature => increased pressure => increased rigidity => increased natural frequency). However, the stiffness of the tire material (rubber) is also influenced by the temperature (increased temperature => softer rubber => lower rigidity => lower natural frequency). It has been shown that the two effects do not compensate each other in their influence on the natural frequency, but the effect is dependent on material, tire temperature and internal pressure. This leads to changes in the natural frequencies in the tire when driving with high temperature fluctuations, which are in the size range of a pressure loss. This is associated with an increased risk of false alarms or non-alarms in case of pressure loss.

In Fig. 1 is a schematic block diagram of an exemplary method is shown, which solves the above problems. The input variables (block E) are the wheel speed sensor signals G) ₁ or variables and / or driving state and / or vehicle information F _{3 associated therewith} in the method according to the present invention. The overall system consists of three process branches A, B, C which can independently trigger a warning (block W): block A: rolling circumference analysis, block B: combination of rolling circumference analysis and frequency analysis, and block C: frequency analysis.

Block A - rolling circumference analysis:

An already known indirect measuring tire pressure monitoring system is used. In this branch A pressure losses are recognizable on a tire. In particular, a system based on the evaluation of the test parameters DIAG, SIDE and AXLE can be used. For this purpose, three test sizes (DIAG, SIDE, AXLE) are determined simultaneously or successively, with each test quantity (DIAG, SIDE, AXLE) being given variables which describe the wheel rotational movements of the wheels, such as the revolution times of a wheel revolution, the rolling circumference, etc. Essentially, the test variables consist of a quotient in whose numerator and denominator the sum of two variables describing the wheel rotational movements stands. In the counter of the test variable DIAG, for example, the sum of the magnitudes of the wheel rotational movement of the two diametrically opposed gonal opposite wheels (eg wheel front left and wheel rear right), whereas in the denominator is the sum of the other sizes of the wheel rotation movements (eg, wheel front right and wheel rear left). In the test quantity SIDE, for example, the variables of the wheel rotational movements of a vehicle side (eg, wheel front right and wheel rear right) are in the counter, whereas in the test parameter AXLE in the counter, the sizes of the wheel rotational movements of the wheels of an axle (eg, wheel front right and wheel front left) stand. The denominators are each formed from the remaining variables of the wheel rotation. These test quantities can be determined at various speed, wheel torque and lateral acceleration or yaw rate intervals. Furthermore, rolling circumference analysis variables for pressure loss warning (ΔDIAG, ΔSIDE, ΔAXLE) between current and learned values are determined. Consequently, these rolling circumference analysis variables are also determined in the intervals from a current value and the learning value associated with the current interval.

Block B - Rolling Circumference Analysis and Frequency Analysis: The combination of the rolling circumference analysis and the frequency analysis makes it possible to detect tire pressure losses on one to three tires.

Block C - frequency analysis:

With a pressure loss on all four tires, the rolling circumference analysis provides only a very limited contribution to pressure loss detection. In this case, the frequency analysis alone provides reliable information and can trigger the warning. With each new and valid result from the rolling circumference analysis, a branch is made into paths A and B. With each new and valid result of the frequency analysis, the paths B and C are traversed. Block B and block C will be discussed in more detail below.

2 shows a schematic block diagram of an exemplary embodiment for combination (block B in FIG. 1) of the two analysis methods rolling circumference analysis I and frequency analysis II. In block 1, a calculation of pressure loss analysis variables is carried out for the rolling circumference analysis I. For this purpose, wheel-individual rolling circumference analysis variables AU ₁ (eg i = 1, 2, 3, 4, the index i stands for one wheel, eg i = 1 means front left, etc.) are calculated from the rolling circumference analysis variables. For this purpose, the method disclosed in document WO 2005/072995 A1 is preferably used. In block 3, pressure loss analysis quantities are calculated in the natural frequency analysis II. For this purpose, at least one wheel-specific eigenfrequency analysis variable Af ₁ (also here the index i is determined for each wheel, corresponding to the rolling circumference analysis variables AU ₁ ), eg a natural frequency or natural frequency shift, eg according to a method of the document WO 2005/072995 A1 or WO 2005/005174 Al. In blocks 2 and 5, a signal plausibility check of the corresponding analysis variables is carried out, for example. The expression of the natural frequency and / or the energy content of the spectrum is investigated and determined, for example, in block 4. For this purpose, for example, a measure is determined which makes a statement about the energy contained in the relevant region of the spectrum. It is also possible to determine a measure for the expression of the eigenfrequency frequency. This measure is particularly important for the load detection of crucial importance. The information from rolling circumference analysis I and frequency analysis II are used to carry out a warning strategy III, which can lead to a warning 10, for example in the form of the activation of a warning lamp.

As already described above, a rapid rash in one or more of the pressure loss analysis variables AU ₁ , Af ₁ may be either an interference effect or an actual fast pressure loss. To distinguish whether it is a disturbance or an actual pressure loss, the time history is evaluated in the signal plausibility check (block 2 or 5). The evaluation is based on the basic idea that the pressure loss analysis variable AU ₁ , Af ₁ usually remains at a fixed level after a rapid decrease, while a sudden pressure loss, caused for example by a puncture during the journey, the pressure loss analysis variable AU ₁ , Af ₁ continues to sink.

In one embodiment, the change of each pressure loss analysis variable AU ₁ , Af ₁ over time is evaluated. If this is above a certain threshold, then one suspects a quick pressure loss or a disturbing influence. A possible warning is initially prevented and the signal is monitored for another time. If the pressure loss analysis variable AU ₁ , Af _{1 continues to increase} in the following observation interval, then a sudden pressure loss can be inferred and the warning is permitted. Stay that way Pressure loss analysis size AU ₁ , Af ₁ but at the elevated level, so closes on a disturbance and the warning is still prevented. Only a further rise can lead to a release of the warning, or a drop below the critical range, the system returns to its normal state (no prevention of a warning) back.

Since at a standstill of the vehicle, the air can be discharged and then a sudden drop in the pressure loss analysis size AU ₁ , Af ₁ would be recorded, but is plausible, such a plausibility check is only active when the vehicle has been driven for a certain time without a stop ,

The warning strategy III is based i.a. on the availability of the system or subsystems. During operation, the following states may occur with regard to the activity of the two systems rolling circumference analysis I and natural frequency analysis II:

Both systems I, II are available and deliver values at short intervals (block 7)

• Only one system is active (Block 8): o Rolling circumference analysis I provides current values, Natural frequency analysis II has not provided any values for some time (restriction due to driving conditions) or has never delivered values (not learned or not yet initialized after starting a trip). o Natural frequency analysis II provides current values, Rolling circumference analysis I has not supplied any values for some time (restriction due to driving conditions) or never delivered values (not learned or not yet initialized after the start of a journey).

The treatment of each state and the transitions between the states is based on the following basic ideas:

Both systems I, II are available only if the distance between two received values from different systems is not greater than a certain time t (for example 1 minute). In this status, a correlation analysis and a mutual influence of the warning thresholds (block 9) can take place.

• The transition between the status "Both systems available" (Block 7) and "Only one system active" (Block 8) is time-controlled or sample-controlled. The warning thresholds are adjusted fluently (block 9). A single system, due to its increased uncertainty with respect to the signal, receives a higher warning threshold than the combination of both systems.

Another aspect of the embodiment schematically illustrated in Fig. 2 is the load detection (block 6). In general, any method that provides information about a load change or a combination of different methods of load detection is suitable for use in a method according to the invention. A load leads to an increase in wheel loads. This leads in the input values of the warning strategy to an increase in the pressure loss analysis variables AU ₁ for the loaded wheels in the rolling circumference analysis I and can thus lead to a false warning of the system. In the exemplary embodiment, therefore, charge detection module 6 initially blocks a warning upon detection of a change in load and causes the system to train compensation values, in particular for the values from the rolling circumference analysis AU ₁ . After compensation, the warning is released again.

In another embodiment, the load detection 6 is realized only from the wheel speed signals G) ₁ . For this purpose, the information from rolling circumference analysis I and frequency analysis II is combined. As already explained above, an additional load leads to an increase in the wheel loads, which leads to an increase in the pressure loss analysis variables AU ₁ for the loaded wheels in the rolling circumference analysis I. In frequency analysis II, increased loading does not affect the natural frequency, but does increase the energy in the spectrum and lead to a more pronounced development of the natural frequency. Since an increased stimulation of the tire by a rougher road has the same effect as an additional load, it is not enough to carry out a consideration of the absolute energy / expressiveness. Rather, the ratio of the energies / expressiveness of the natural frequency between the front and rear axle to form.

The basic idea of this exemplary embodiment of a load detection module 6 will be described below using the example of a Axle load explains:

• If: after a standstill and a load on the rear axle, the rolling circumference analysis I indicates a pressure loss on the rear axle,

• and: the natural frequency analysis II shows no significant shift of the natural frequency on the rear axle,

• and in addition: either the absolute value of the energy / the expressiveness of the spectrum at the rear wheels has risen compared to a previously learned state or the ratio of these quantities has changed from front to back,

• then: the system detects a possible load change and either adjusts the warning thresholds in the warning field (block 9) or calculates a compensation value for the rear axle values from the rolling circumference analysis I.

Another aspect of the embodiment schematically illustrated in FIG. 2 is the warning decision (block 9), in which it is decided whether or not a pressure loss warning 10 is issued. An important point here is the influencing of the thresholds of the individual pressure loss analysis variables AU ₁ , Af ₁ or combined pressure loss analysis variables for pressure loss detection.

If both systems are active (block 7), the following example method will provide both the information (absolute values) of the individual systems and the correlation the two systems linked together. The two wheel-specific pressure loss analysis variables AU ₁ , Af ₁ from rolling circumference analysis I and natural frequency analysis II of a tire (i is fixed) are linked together in a warning field 14 to form a single pressure loss analysis variable. This is shown schematically in FIG. The pressure loss analysis variable AU _{1 of} a tire from the rolling circumference analysis I is plotted on the x axis and the pressure loss analysis variable Af _{1 of} a tire from the natural frequency analysis II is plotted on the y axis. Below the connecting line of the points 13, 11, 12 (warning threshold WS), no pressure loss warning 10 is output, above the connection line the combined pressure loss analysis quantity is more than 100% and a warning 10 is issued.

The basic idea of the warning field 14 is that only if both pressure loss analysis variable AU ₁ , Af ₁ indicate a pressure loss results in a high combined pressure loss analysis parameter. If only one system I or II indicates a pressure loss, it must have a very high value in order to trigger a warning 10. Characteristic of the exemplary warning field are the three points 11, 12 and 13:

Item 11 - Intersection:

If both values are above this point, the combined pressure loss analysis size is greater than 100%. • 12 - puncture point rolling circumference analysis axis:

If the natural frequency analysis II does not indicate a pressure loss, the rolling circumference analysis variable AU ₁ must indicate a value above this point for the combined pressure loss analysis quantity to become greater than 100%. • 13 - puncture point eigenfrequency analysis axis:

If the rolling circumference analysis parameter I indicates no pressure loss, the natural frequency analysis must indicate a value Af ₁ above that point in order for the combined pressure loss analysis to become larger than 100%.

Thus, first a wheel-individual correlation between the two systems I and II is established.

In addition, in another exemplary embodiment, which is shown schematically in FIG. 4, an evaluation is made to what extent rolling circumference analysis I and natural frequency analysis II indicate the same pressure loss scenario. For this purpose, e.g. In block 15, a correlation K is calculated. The position of the warning threshold WS can then be changed as a function of the correlation variable K, as is indicated schematically in FIG. If a very good correlation is obtained, then one has a high degree of confidence in the values determined and the threshold WS is lowered (in the direction of the origin in FIG. 4). If the correlation is bad, the warning threshold WS is shifted upward (direction right above in FIG. 4).

In a transition from the state "both systems active" (block 7) to "only one system active" (block 8), the pressure loss value (the pressure loss analysis size) of the inactive system is successively reduced to zero. Likewise, the puncture point of the warning field on the axis of the active system is increased by a factor. This will give you the ability to alert even if only one system is available, while reducing the risk of misleading. In a further exemplary embodiment, which is shown schematically in FIG. 5, the maximum 16 of the combined pressure loss analysis variables from four warning fields 14 (one per wheel) is used to produce a warning 10. If this maximum 16 with a sufficient statistical significance is above 100%, the warning 10 is output, for example in the form of a warning lamp.

Since in a rolling circumference analysis the differences, quotients or the like of the rotational speeds (or directly related variables, such as orbital periods or circumferences) are evaluated among each other, the rolling circumference analysis is almost "blind" in the case of a four-wheeled pressure loss For the warning of a simultaneous four-wheeled pressure loss Therefore, as already mentioned above, only the information, eg, the pressure loss analysis quantity (s), is evaluated from the frequency analysis (block C in Fig. 1) As an example of a pressure loss analysis quantity from the frequency analysis, the natural frequency shift is used in the following description However, this is possible with a pressure loss analysis variable, which results from frequency shift and further spectrally describing variables, as described in more detail, for example, in the document WO 2005/005174 A1, which according to the example has a frequency shift for each wheel.

The following conditions for a warning 10 must be met in this branch C:

1. All four pressure loss analysis quantities from the frequency analysis (frequency shifts) must have a pressure show above a defined threshold (eg 80% of a warning threshold).

2. At least one tire must show a value above the 100% threshold.

Furthermore, a plausibility check of the result with the rolling circumference analysis variables can take place. These must not show any significant pressure loss at individual positions.

Another aspect of the frequency analysis is a compensation of the temperature influence. According to the example, the natural frequency f _k (where the index k is for VL: front left, front right VR, rear left HL, or rear right HR) of the tire is taught together with a calculated tire temperature. From this ensemble, a compensation quantity for the temperature influence is determined, which is applied to the determined natural frequencies.

FIG. 6 shows a schematic block diagram for temperature compensation in a frequency analysis. At the beginning, before a compensation value is present, an empirical mean value (eg -0.5 Hz / 10 ° C.) is assumed as basic compensation 19. During learning is then from various driving, Fahrzustands-, vehicle and environmental information X _n , such as outdoor temperature, service life, coolant temperature, driving speed, driving profile, etc., using a temperature model 17 a tire temperature T _Rei fen calculated. In addition, the natural frequencies of the wheels f _VL , f _VR , f _HL , f _{HR are} determined accordingly. If temperature / frequency values are available, a correction factor of 18 is set. learns. This is used to determine from the basic compensation 19 a current temperature compensation value 20 with which the temperature-compensated natural frequencies f vi, f VR, f HL, f HR are determined.

When learning the correction factor 18, an evaluation of the spread of the temperature T _Rei f _e n is performed. The correction factor 18 is only accepted if the spread of the learned temperature / frequency ensemble with respect to the temperature T _Rei f _e n (eg lowest temperature to highest temperature and sufficient number of value pairs above this range) is large enough.

The temperature model 17 used to calculate the tire temperature T _Rei fen, for example according to the following information:

• Outside temperature T _outside , available either via a temperature sensor in the control unit or via CAN messages, such as outside air temperature and intake air temperature,

• Service life of the vehicle: Estimation sometimes via the coolant temperature or engine temperature T _Engine in combination with the outside temperature T _Outside , if no service life is available,

• Driving profile, available from the speed signal v, yaw rate or lateral acceleration and drive torque. In addition, calculated quantities such as e.g. Mileage since "Ignition-On", and

• Rain sensor or dew point sensor information to help you understand the wetness of the road. This information is linked by means of a temperature model 17, which in a first embodiment

• • • the heat flow Q through flexing Q _Wa i _k 'Convection Q _Cθnvect i _on

radiant heat Q _Rac ii _at i _on , and from this a

calculated at room temperature. In another term Qv _eh i _c i _e i _t i c _ond _on environmental condition influences the vehicle, such as brake temperature and engine temperature, taken into account.

Possible calculation equations are: Radiation / radiant heat: _n _ _A. ( _T 4 _ "4 \ _ ( _T 4 _" 4 \

^ Radiation ^t u - - \ - ⁱ - _{From seri} Tires / ^u s V- ¹ Au _S sen - "- Tires /

Convection:

• /

Qconvection = « _k ^■ Vv ^■ (ITT Outside - Tire,

Flexing work:

Q _Walk = fmgv = fF _z -v vehicle conditions / vehicle heat input:

O VehicleCondition = ^ -f ( ^v T ^x Brake 'T Angine' ¹ 'I

With

8: emissivity,

G: Stefan Boltzmann constant,

A: radiating surface of the tire,

CCs: proportionality constant of radiant heat, α _k : constant of proportionality of convection, f: proportionality constant of rolling resistance,

F _z : wheel load, v: speed, T _outside : outside temperature,

T _Rei fen: tire temperature, and f (t ake _Br, T _Engine, ...): a function of brake temperature T _Br ake, the

_Engine temperature T _engine and other sizes.

The tire temperature T _Rei f _e n can then be calculated from:

With tires: heat capacity of the tire.

FIG. 7 shows schematically an exemplary method for calculating the tire temperature T _Rei f _e n according to the above equation. From outside temperature T _outside , driving speed v, brake temperature T _brake , engine temperature T _engine and a start value T _st kind for the tire temperature, the four warning values

• • • • mef lussbeiträge _Wa Q ik 'Qconvection r QRadiation and Qvehiciecondition ^¬ be counted, added up in block 21, divided by the heat capacity C _fen _Re i in block 22 and in block 23 over the time t in ^¬ tegriert. The resulting tire temperature T _tire becomes

Calculation of new heat flow contributions Q _Cθnvect i _on , Q _Rad i _at i _on ^{¬ used} .

In a particularly simple embodiment of the

Radiation _fraction Q _{Radiat; LOri} neglected. To compensate for the lack of temperature decrease, a minimum velocity v is assumed to be the input for the convection equation.

To determine a start value T _st art, the plausibility values from the service life are used.

According to a further embodiment, a consideration of the temperature influence is also carried out for the analysis variables ΔDIAG, ΔSIDE, ΔAXLE of the rolling circumference analysis. For this purpose, the test size DIAG, SIDE, AXLE are taught together with a calculated tire temperature.

In a further embodiment, the temperature compensation described above is also performed in the frequency analysis II of the combined method B.

Claims

claims

1. A method for indirect tire pressure monitoring, in which a rolling circumference analysis of the tires, in which from currently determined and learned test variables describing the Raddrehbewegung the wheels, rolling circumference analysis variables (.DELTA.DIAG, .DELTA.SIDE, .DELTA.AXLE) are determined, and carried out a frequency analysis of the natural vibration behavior of at least one tire be in which at least one frequency analysis variable (f _k ) is determined, characterized in that to warn a tire pressure loss an evaluation of the rolling circumference analysis (A) and the natural frequency analysis (C) and a combined evaluation (B) of both analysis methods is made.

2. The method according to claim 1, characterized in that a natural frequency analysis is performed for each tire.

3. The method according to claim 1 or 2, characterized in that in the combination of both analysis methods (B) each for rolling circumference analysis (I) and frequency analysis (II) wheel-specific pressure loss analysis quantities (AU ₁ , Af ₁ ) are determined.

4. The method according to at least one of claims 1 to 3, characterized in that in the combination of both analysis methods (B) warning thresholds (WS) each of the two analysis methods in dependence on the analysis variables (AU ₁ , Af ₁ ), in particular the wheel-individual pressure loss analysis variables, which are selected in each case different method.

5. The method according to at least one of claims 1 to 3, characterized in that in the combination of both analysis methods (B) warning thresholds (WS) of each of the two analysis methods in dependence on the analysis variables

(AU ₁ , Af ₁ ), in particular the wheel-individual pressure loss analysis variables, the other method and a correlation measure (K) between the two analysis methods are selected.

6. The method according to claim 4 or 5, characterized in that the warning thresholds (WS) as a function of the availability (7, 8) of the analysis variables (AU ₁ , Af ₁ ), in particular the pressure loss analysis variables are changed.

7. The method according to at least one of claims 3 to 6, characterized in that for at least one wheel, in particular for each wheel, a combined wheel-individual pressure loss analysis variable, in particular on the basis of a warning field (14) is determined, in which the pressure loss analysis variables (AU ₁ , Af ₁ ), and especially the warning thresholds (WS), both analysis methods are received.

8. The method according to claim 7, characterized in that a warning (10) with respect to a tire pressure loss as a function of at least two, in particular of all, the combined wheel individual pressure loss analysis quantities is output.

9. The method according to claim 8, characterized in that the warning (10) based on the maximum (16) of the combined wheel-specific pressure loss analysis variables.

10. The method according to at least one of the preceding claims, characterized in that for at least one of the determined analysis variables (AU ₁ , Af ₁ ), in particular Abrollumfangsanalysegröße, frequency analysis variable, pressure loss analysis variable or combined pressure loss analysis variable, a plausibility check (2, 5) of the determined value based on time course of the analysis size is performed.

11. The method according to claim 10, characterized in that based on the result of the plausibility check (2, 5) a decision is made as to whether there is a pressure loss or a disturbing influence.

12. The method according to at least one of the preceding claims, characterized in that the loading and / or a load change of the vehicle is determined (6).

13. The method according to claim 12, characterized in that the detection of the loading and / or loading change

(6) determines from a combination of at least one information of a rolling circumference analysis (I) of the wheels with at least one information of a frequency analysis (II) of the natural vibration behavior of at least one tire becomes .

14. The method according to claim 13, characterized in that in the frequency analysis (II) for at least one wheel, in particular for each wheel, a measure that represents a measure of the expression of the natural frequency, in particular the energy content of the spectrum in the natural frequency range, is determined, and that the measure size (s), in particular ratios of measures, for detecting the loading and / or loading change (6) is / are used.

15. The method according to claim 14, characterized in that the ratio of the Maßgrößen between front and rear wheels is used.

16. The method according to at least one of claims 12 to 15, characterized in that the determination of a loading and / or load change (6) to a change in the warning thresholds (WS) of the analysis variables (AU ₁ , Af ₁ ), in particular the load-dependent pressure loss analysis variables, and / or to a compensation of the analysis variables, in particular the load-dependent pressure loss analysis variables, leads.

17. The method according to at least one of the preceding claims, characterized in that, in particular in a frequency analysis (C, II), a temperature compensation (20) of an analysis variable (f _k , ΔDIAG, ΔSIDE, ΔAXLE), in particular the natural frequency of at least one tire is carried out.

18. The method according to claim 17, characterized in that for determining a compensation variable, in particular the quotient change of the frequency analysis variable by temperature change, one by means of a temperature model

(17) calculated tire temperature (T _tire ) is used.

19. The method according to claim 18, characterized in that the temperature model (17) at least one of the following heat changes considered: heat flow through Walkar

of the tire (Q _Waik ), heat flow through convection

(Qc _onvect _on ) ι heat flow through radiation of the tire

(Q _wheel i _at i _on) r Heat flow by entry of the vehicle

'QvehicleCondition / •

20. The method according to claim 18 or 19, characterized in that for learning the compensation quantity, the analysis variable (f _k , ΔDIAG, ΔSIDE, ΔAXLE), in particular natural frequency, together with the calculated tire temperature (T _Rei fen) is considered over one or more trips ,

21. The method according to at least one of claims 18 to 20, characterized in that the tire temperature (T _tire ) is calculated taking into account at least two of the following variables: outside temperature (T _outside ), Tempera ^¬ tur in a control unit, engine intake air temperature, coolant temperature , _Engine temperature (T _Engine ), brake temperature (T _Br ake), vehicle life, driving profile since the ignition is switched on, in particular vehicle speed (v), yaw rate, lateral acceleration, drive torque and / or driven kilometers, surroundings sensor information, in particular rain sensor and / or dew point sensor information.

22. Computer program product, characterized in that it defines an algorithm which comprises a method according to any one of claims 1 to 21.